Method for forming an orthopedic implant surface configuration

ABSTRACT

The present invention is a specialized orthopedic implant having an exterior surface for engaging bone. The surface comprises arrayed projections having at least one forward facing facet directed at least in part toward the leading end of the implant and at least one rearward portion directed at least in part toward the opposite trailing end of the implant. Each of the forward facet and rearward portion has a length and a slope. The length of the forward facet is longer than the length of the rearward facet. The slope of the rearward facet is steeper than the slope of the forward facet. The surface projections also have opposed side facets directed generally toward the sides of the implant. The side facets are located between the forward facet and rearward facet and converge toward each other in a direction away from the base of the surface projections. The surface may also include projections having left and right forward side facets and a rearward facet. The surface further may include projections having left and right rearward side facets and a forward facet.

RELATED APPLICATION

This application is a continuation of application Ser. No. 09/572,518,filed May 17, 2000; which is a continuation-in-part of application Ser.No. 09/457,228, filed Dec. 8, 1999, now U.S. Pat. No 6,827,740; all ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Description of the Related Art

The present invention relates to orthopedic implants for placement atleast in part into bone, or for placement at least in part betweenadjacent bones or bone portions of a human skeleton. The orthopedicimplants of the present invention have a specialized surface forengaging bone.

Vital to the functioning of such orthopedic implants is their ability toremain properly located within bone after installation. In U.S. Pat.Nos. 5,593,409 and 5,609,635, Michelson described the use of surfaceroughenings, such as knurling or ratcheting on the opposed upper andlower vertebral body engaging surfaces of interbody spinal fusionimplants. Knurling has been particularly beneficial for increasing thegrip of the implant surface to the bone of the adjacent vertebral bodiesin a rather uniform manner without a directional bias. Orthopedicimplants inserted at least in part into bone, have a propensity to movein a particular direction, which is opposite to their path of insertion,because this is the path of least resistance. Such propensity to move isfurther increased when the implant has an overall configuration that istapered along at least a portion of its length such that the boneengaging surfaces of the implant are in angular relationship to eachotherand are spaced further apart at the implant's trailing end than atthe implant's leading end. In such circumstances where it is desirablethen to gain stability in resistance to a particular direction ofmovement of the orthopedic implant, the use of a plurality of forwardfacing ratchetings on the implant's bone engaging surfaces has beenpreferable to the previously described knurling for that purpose.

The term “ratcheting” as used herein is defined as a plurality ofangular teeth or ridges or protrusions projecting from the surface of animplant to resist motion of the implant at least in one direction. Thephrase “forward facing ratchetings” as used herein is defined as aratcheting having at least one forward facing facet having a lengthgreater than a rearward facing facet and an angle from the implantsurface from which the forward facing facet arises that is less steepthan the angle of the rearward facet. On an implant surface, forwardfacing ratchetings facilitate the insertion of the implant in onedirection and after insertion, resisting movement of the implant in adirection opposite to the direction of insertion. An example of forwardfacing ratchetings of the prior art is shown in partial fragmentary viewin FIGS. 24A and 24B, generally referred to by the reference numeral 50.

Knurled surfaces of the related art provide some stability in alldirections, but lack the ability to resist a particular direction ofmotion preferentially. The above-described ratcheted surface bestresists motion in a particular direction. There exists a need for animproved orthopedic implant surface configuration, wherein the boneengaging surfaces of the implant are configured to be resistant toimplant movement in all directions, and preferentially in particularlyone direction.

SUMMARY OF THE INVENTION

The present invention relates to orthopedic implants having aspecialized surface configuration on at least a portion of the exteriorsurfaces adapted for engaging bone, including adjacent bones and boneportions, into which the implant is to be implanted. Such an implantsurface configuration has utility with a wide variety of shapes oforthopedic implants where enhanced skeletal fixation is desired. Such animplant surface configuration can provide for enhanced stability,increased surface area, and a surface for the delivery of fusionpromoting substances other than bone. In a preferred embodiment, theimplant surface can provide for resisting motion in all directions, andparticularly in at least one direction, such as counter to the directionof insertion of the implant.

While various embodiments of the present invention are presented by wayof example only and not limitation, common to each of them is that thesurface configuration incorporates a plurality of spatially integratedsurface projections having at least one forward facing facet directed atleast in part toward the leading end of the implant and at least onerearward portion directed at least in part toward the opposite trailingend of the implant. By way of example and not limitation, the rearwardportion may be a facet, a line, or an edge of the rearward aspect of thesurface projection formed where two facets come together. Each of theforward and rearward facets have a length and a slope. The length of theforward facet is longer than the length of the rearward facet. The slopeof the rearward facet is steeper than the slope of the forward facet. Invarious embodiments, the surface projections also have opposed sidefacets directed generally toward the sides of the implant. The sidefacets are located between the forward facet and rearward facet and mayconverge toward each other in a direction away from the base of thesurface projections. The surface comprises multifaceted ratchetedprojections that are organized in geometrically disposed fields orarrays which are at a minimum located on at least a portion of the boneengaging surfaces of the implant. From the teachings disclosed herein,it is appreciated that the surface projections can be geometricallyarranged in a pattern wherein at least a portion of the projection isaligned along a longitudinal, horizontal, diagonal, or curved line. Thebone engaging surfaces of the implant can be at least in part arcuate orplanar and can converge along a portion or all of the length of theimplant.

In various preferred embodiments of the present invention, the rearwardfacets of the surface projections can be perpendicular or at anglesgreater or less than 90 degrees to exterior surface of the implant fromwhich the projections arise. The opposed side facets of the surfaceprojections can have at least a first portion in a plane at an angle tothe longitudinal axis of the implant. The opposed side facets canintersect each other, and can converge to form a peak at the top of eachof the surface projections. The peaks can be aligned along lines thatare perpendicular, parallel, or diagonal to the longitudinal axis of theimplant. The surface projections can be cleaved such as by longitudinaland/or horizontal cuts to increase the number of exposed sides of theprojections and thus increase the available surface area to contact andengage the bone adjacent the implant and increase the number of recessedareas to contain material such as fusion promoting substances forexample. Alternatively, the peaks of each surface projection can becleaved, truncated, or flattened at least in part.

The surface projections can include a left forward side facet and aright forward side facet directed toward the leading end and sides,respectively, of the implant. Similarly, the surface projections caninclude a left rearward side facet and a right rearward side facetdirected toward the trailing end and sides, respectively, of theimplant. The side facets of adjacent surface projections can be spacedapart to define a groove therebetween. A plurality of adjacent surfaceprojections can be spaced apart to form a plurality of grooves that canbe parallel or at an angle to the longitudinal axis of the implant,wherein the angle can be less than 90 degrees. The grooves can have ahorizontal cross section that is a V-shape, U-shape, or a box-likeshape, for example.

Sequential projections can be positioned on an implant wherein eachsurface projection has forward facing facets facing the same direction,such that consecutive projections are oriented forward facing facet torearward facing facet. The lower most portion of the slope of theforward facing facet of a first surface projection in a sequence can becoincident with the rearward facet of the next surface projection in thesequence. Alternatively, the forward facet of a first surface projectionand the rearward facet of the next surface projection in a sequence canbe spaced apart and the space can be at least in part flat, curved, orany other surface contour suitable for the intended use. The surfaceprojections can be oriented relative to one another to form fields orarrays that further can be geometrically disposed relative to oneanother, preferably in a pattern wherein at least a portion of theprojection is aligned along a longitudinal, horizontal, diagonal, orcurved line.

The surface configuration of the present invention can be formed bycasting, machining, or any other techniques known to one of ordinaryskill in the art. The present surface configuration may readily bemachined by milling the implant surface from side to side, across thebone engaging surfaces, to form ratchetings generally disposedperpendicular to the long axis of the implant and generally formedfacing to the insertion end of the implant. The ratchetings may be crossmachined with an angled cutting face to form grooves passing through theratchetings. For example, a milling machine having a cutting tool, witha V-shaped profile, can be run through the plurality of ratchetingsparallel to the longitudinal axis of the implant to form theabove-described surface. In a preferred embodiment, the V-shaped cuttingtool of the milling machine has opposed cutting faces with an angle ofapproximately 90 degrees to each other, which faces are each at a45-degree angle to the plane of the surfaces being machined. Withoutdeparting from the scope of the present invention, the angle of thecutting faces can be more or less than 90 degrees, and the angle of thecutting face to the surface to be cut can be more or less than 45degrees. It is appreciated that rather than the cutting element beingrun parallel to the longitudinal axis of the implant, the cuttingelement could be run at some other angle. By way of example only and notlimitation, this angle could be at 45 degrees to the longitudinal axisof the implant and to the projections. Each surface projection couldthen be formed by a cutter crossing in two passes to form two grooves ata 90 degree angle to each other.

The surface configuration of the implant of the present invention may beincorporated into various types of orthopedic implants. Such orthopedicimplants may be for securing a prosthetic device implanted into bone,may be for the purpose of healing bone portions or for achieving fusionof bones, or for stabilizing a device to space apart and allow motionbetween the adjacent bones or bone portions. Such orthopedic implantsmay comprise any artificial or naturally occurring material appropriatefor the intended purpose. Such materials would include, but are notlimited to, implant quality metals, including, but not limited to,titanium and its alloys, surgical grade plastics and plastic compositeswhich may or may not be bioresorbable, ceramics, and cortical bone. Someexamples of interbody orthopedic implants that may benefit from thepresent teaching, include but are not limited to any artificial jointcomponent having an intramedullary stem, such as but not limited to, hipreplacements, shoulder replacements, knee replacements, and fingerjoints; and medical prosthetic implants for replacing a lost portion ofa long bone.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of an orthopedic implant having a surfaceconfiguration in accordance with the present invention.

FIG. 2 is a side elevation view of the orthopedic implant of FIG. 1.

FIG. 3 is a side elevation view of the interbody orthopedic implant ofFIG. 1 installed in an implantation site formed in bone shown in partialcross-section.

FIG. 4 is an enlarged fragmentary top plan view of an implant surface ofone embodiment of the present invention from a view taken along area 4of FIG. 1.

FIG. 5 is a fragmentary side elevation view of the implant surface ofFIG. 4 from a view taken along area 5 of FIG. 2.

FIG. 6 is a fragmentary end elevation view of FIG. 4.

FIG. 7 is a fragmentary perspective view of the implant surface of FIG.4.

FIG. 8 is an enlarged fragmentary top plan view of a second embodimentof the implant surface of the present invention from a view taken alongarea 8 of FIG. 1.

FIG. 9 is a fragmentary side elevation view of the implant surface ofFIG. 8 from a view taken along area 9 of FIG. 2.

FIG. 10 is a fragmentary end view of the implant surface of FIG. 8.

FIG. 11 is a fragmentary perspective view of the implant surface of FIG.8.

FIG. 12 is an enlarged fragmentary top plan view of a third embodimentof the implant surface of the present invention from a view taken alongarea 12 of FIG. 1.

FIG. 13 is a fragmentary side elevation view of the implant surface ofFIG. 12 from a view taken along area 13 of FIG. 2.

FIG. 14 is a fragmentary end view of FIG. 12.

FIG. 15 is a fragmentary perspective view of the implant surface of FIG.12.

FIG. 16 is an enlarged fragmentary top plan view of a fourth embodimentof the implant surface of the present invention from a view taken alongarea 16 of FIG. 1.

FIG. 17 is a fragmentary side elevation view of the implant surface ofFIG. 16 from a view taken along area 17 of FIG. 2.

FIG. 18 is a fragmentary end view of FIG. 16.

FIG. 19A is an enlarged fragmentary perspective view of the implantsurface of FIG. 16.

FIG. 19B is an enlarged fragmentary perspective view of a variation onthe second and third surface projections of the fourth embodiment of theimplant surface of the present invention with a cleave therethrough.

FIG. 20 is an enlarged fragmentary top plan view of a fifth embodimentof the implant surface of the present invention from a view taken alongarea 20 of FIG. 1.

FIG. 21 is a fragmentary side elevation view of the implant surface ofFIG. 20 from a view taken along line 21 of FIG. 2.

FIG. 22 is a fragmentary end view of FIG. 20.

FIG. 23 is an enlarged fragmentary perspective view of the implantsurface of FIG. 20.

FIGS. 24A and 24B are perspective and side elevation views,respectively, of a prior art implant surface having forward facingratchetings.

DETAILED DESCRIPTION OF THE DRAWINGS

As shown in FIGS. 1–7, an orthopedic implant 100, in the form of a hipprosthesis in this example, has a leading end 102, a trailing end 104,and an exterior surface 106. Implant 100 may converge from trailing end104 to leading end 102 along a longitudinal axis L of implant 100 asshown, or may diverge, be parallel, or any combination thereof. Exteriorsurface 106 is configured to be placed against and in contact orengagement with the bone B, including adjacent bones or bone portions,of a human skeleton. It is appreciated that the surface configuration ofthe present invention is not limited to a hip prosthesis and may beincorporated in other types of orthopedic implants including suchimplants placed between adjacent bones or adjacent bone portions of thehuman skeleton. Exterior surface 106 may include large and/or smallopenings 114, 116 to permit bone growth into and through implant 100.Exterior surface 106 of implant 100 can be generally planar, or can bearcuate as shown in the Figures, or any other configuration suitable forthe desired use.

As shown in detail in FIGS. 4–7, at least a portion of exterior surface106 of implant 100 has a surface configuration generally referred to bythe numeral 120. In accordance with a first embodiment of the presentinvention, surface configuration 120 includes surface projections 122configured to facilitate insertion of implant 100 into an implantationsite while resisting expulsion of implant 100 in a direction opposite tothe direction of insertion. Each of surface projections 122 has anangled forward facet 124 directed at least in part toward leading end102 of implant 100 and a rearward facet 126 directed at least in parttoward trailing end 104 of implant 100. Forward facet 124 has a lengthgreater than the length of rearward facet 126. Rearward facet 126 has aslope that is steeper than the slope of forward facet 124. In thisembodiment, the base of rearward facet 126 forms an angle ofapproximately 90 degrees with respect to exterior surface 106 of implant100. It is appreciated that the angle of the base of rearward facet 126with respect to exterior surface 106 of implant 100 may be perpendicularto, greater than perpendicular to, or less than perpendicular to thebase of the surface where the facet arises. Forward facet 124 forms anangle in the range of approximately 10 to 60 degrees, with 25–45 degreesbeing preferred, with respect to exterior surface 106. Each one ofsurface projections 122 also has a left side facet 132 and a right sidefacet 134 directed toward the sides of implant 100.

In this embodiment of surface configuration 120, a plurality of surfaceprojections 122 are spaced apart laterally (side to side) bylongitudinal grooves 130 formed along the longitudinal axis L of implant100. In one embodiment, longitudinal grooves 130 have a V-shapedhorizontal cross-section. The lower most portions of left and right sidefacets 132, 134 of consecutive side-by-side projections 122 can becoincident with each other or may be spaced apart, any spacetherebetween can be at least in part flat, curved, sloped or otherwiseconfigured. Each surface projection 122 has left and right side facets132, 134 that converge to form a high point or peak 136 at the top ofeach surface projection 122. Each peak 136 can be aligned along linesthat are perpendicular, parallel, and/or diagonally oriented tolongitudinal axis L of implant 100. The left and right side facets 132,134 resist side-to-side motion of implant 100 after it is inserted intothe implantation space. Peaks 136 engage the bone B adjacent to implant100 in the implantation site. It is appreciated that in a variation ofthe present invention, the peaks may be modified such as to be truncatedor cut off to have a broader rather than shaper upper most surface.Moreover, the peaks can be cleaved in one or more directions so as toincrease the surface area useful for engaging bone. The relieved areasof the cleaved projections are useful for containing and carrying fusionpromoting substances other than bone such as bone morphogenetic proteinsand genetic materials coding for the production of bone, or bone itselfwhich could by way of example be in the form of a paste. It is furtherappreciated that for all the various embodiments of the surfaceconfiguration of the present invention, longitudinal grooves 130 canhave horizontal cross-sections in a variety of configurations such as,without limitation, square-shaped or U-shaped configurations.

Sequential projections can be positioned on an implant wherein eachsurface projection has forward facing facets facing the same directionsuch that consecutive projections are oriented forward facing facet torearward facing facet. The lower most portion of the slope of theforward facing facet of a first surface projection in a sequence can becoincident with the rearward facet of the next surface projection in thesequence. Alternatively, the forward facet of a first surface projectionand the rearward facet of the next surface projection in a sequence canbe spaced apart and the space can be at least in part flat, curved, orany other surface configuration suitable for the intended use. Thesurface projections can be oriented relative to one another to form anarray and are preferably geometrically disposed relative to one anotherin a pattern wherein at least a portion of the projection is alignedalong a longitudinal, horizontal, diagonal, or curved line. Further, itis appreciated that the surface of the present invention can be usefulwith orthopedic implants of various configurations, includingconfigurations wherein at least one of leading end, trailing end, andsides of the orthopedic implant is curved. By way of example and notlimitation, the leading end, trailing end, and sides of the orthopedicimplant can form an oval, an oblong, a circle, or other geometric shape.

As shown in FIGS. 8–11, a second embodiment of the surface configurationof the present invention is generally referred to by the numeral 220.Surface configuration 220 includes surface projections 222 to facilitateinsertion of implant 100 into an implantation site while resistingexpulsion of implant 100 in a direction opposite to the direction ofinsertion. Each of surface projections 222 has an angled forward facet224 directed at least in part toward leading end 202 of implant 100 anda rearward facet 226 directed at least in part toward trailing end 204of implant 100. Forward facet 224 has a length greater than the lengthof rearward facet 226. Rearward facet 226 has a slope that is steeperthan the slope of forward facet 224. In this embodiment, the base ofrearward facet 226 forms an angle of approximately 45 degrees withrespect to exterior surface 206 of implant 100. Each one of surfaceprojections 222 has a left side facet 232 and a right side facet 234directed toward the sides of implant 100, and forward facet 224 andrearward facet 226.

In this embodiment of surface configuration 220, longitudinal grooves230 have a V-shaped horizontal cross-section. The lower most portions ofleft and right side facets 232, 234 of consecutive side-by-sideprojections 222 can be coincident with each other or may be spacedapart, any space therebetween can be at least in part flat, curved,sloped or otherwise configured. Each surface projection has left andright side facets 232, 234 that converge to form a high point or peak236 at the top of each surface projections 222. Each peak 236 can bealigned along lines that are perpendicular, parallel, and/or diagonallyoriented to the longitudinal axis L of implant 100. The left and rightside facets 232, 234 resist side-to-side motion of implant 100 after itis inserted into the implantation space. Peaks 236 engage bone Badjacent to implant 100 in the implantation site.

As shown in FIGS. 12–15, a third embodiment of the surface configurationof the present invention is generally referred to by the numeral 320 isshown. Surface configuration 320 includes surface projections 322 tofacilitate insertion of implant 100 into an implantation site whileresisting expulsion of implant 100 in a direction opposite to thedirection of insertion. Each of surface projections 322 has an angledforward facet 324 directed at least in part toward leading end 302 ofimplant 100 and a rearward facet 326 directed at least in part towardtrailing end 304 of implant 100. Forward facet 324 has a length greaterthan the length of rearward facet 326. Rearward facet 326 has a slopethat is steeper than the slope of forward facet 324. In this embodiment,the base of rearward facet 326 is “back cut” to form an angle greaterthan 90 degrees with respect to exterior surface 306 of implant 100. Theconfiguration of rearward facet 326 further enhances resistance ofmotion of the implant in a direction opposite to the direction ofinsertion. It is appreciated that the angle of the base of rearwardfacet 326 with respect to exterior surface 306 of implant 100 can be anyother angle suitable for the intended purpose of the present invention.Each one of surface projections 322 has a left side facet 332 and aright side facet 334 directed toward the sides of implant 100, and aforward facet 324 and a rearward facet 326.

In this embodiment of surface configuration 320, longitudinal grooves330 have a V-shaped horizontal cross section. The lower most portions ofleft and right side facets 332, 334 of consecutive side-by-sideprojections 322 can be coincident with each other or may be spacedapart, and any space therebetween can be at least in part flat, curved,sloped or otherwise configured. Each surface projection 322 has left andright side facets 332, 334 that converge to form a high point or peak336 at the top of each surface projection 322. Each peak 336 can bealigned along lines that are perpendicular, parallel, and/or diagonallyoriented to the longitudinal axis L of implant 100. The left and rightside facets 332, 334 resist side-to-side motion of implant 100 after itis inserted into the implantation space. Peaks 336 engage bone Badjacent to implant 100 in the implantation site.

As shown in FIGS. 16–19B, a fourth embodiment of the surfaceconfiguration of the present invention is generally referred to by thenumeral 420. Surface configuration 420 includes surface projections 422configured to facilitate insertion of implant 100 in the direction ofinsertion into an implantation site while resisting expulsion of implant100 in a direction opposite to the direction of insertion. Each ofsurface projections 422 has an angled forward facet 424 directed towardleading end 402 of implant 100 and a rearward portion 426 directedtoward trailing end 404 of implant 100. Forward facet 424 has a lengthgreater than the length of rearward portion 426. Rearward portion 426has a slope that is steeper than the slope of forward facet 424. In thisembodiment, the base of rearward portion 426 forms an angle ofapproximately 90 degrees with respect to exterior surface 406 of implant100. Rearward portion 426 can be a portion of surface projection 422,such as a facet, an edge, or a line for example. Each one of surfaceprojections 422 has a left side forward facet 450, a right side forwardfacet 452, a left side rearward facet 454, and a right side rearwardfacet 456 directed toward the front and sides, and directed toward therear and sides of implant 100, respectively, and forward facet 424 andrearward portion 426.

Surface configuration 420 can further include a second plurality ofsurface projections 460 having at least a left forward side facet 462and a right forward side facet 464 directed at least in part towardleading end 402 and sides of implant 100, respectively, and at least onerearward facet 466 directed at least in part toward trailing end 400.Left and right forward side facets 462, 464 have at least a firstportion in a plane at an angle to the longitudinal axis of implant 100.Second surface projections 460 can be interspersed with surfaceprojections 422.

Surface configuration 420 can further comprise a third plurality ofsurface projections 470 having at least a left rearward side facet 472and a right rearward side facet 474 directed at least in part towardtrailing end 404 and sides of implant 100, respectively, and at leastone forward facet 476 directed at least in part toward leading end 402.Left and right rearward side facets 472, 474 have at least a firstportion in a plane at an angle to the longitudinal axis of implant 100.Third surface projections 470 can be interspersed with surfaceprojections 422 and/or second surface projections 460. Surfaceprojections 422 may have a length approximating the combined length ofsecond surface projections 460 and third surface projections 470.

In this embodiment, surface configuration 420 has angled grooves 440 a–kthat form a plurality of surface projections 422. In this example,angled grooves 440 a–k are formed at an angle that is approximately 45degrees to longitudinal axis L of orthopedic implant 100 and in thisexample, angled grooves 440 a–k are approximately 90 degrees to oneanother. The angled grooves 440 a–k can be formed, if machined, by firstpassing a cutting element at a 45 degree angle to the longitudinal axisL of implant 100 and then passing the cutting element at a 90 degreeangle to the path of the first pass of the cutting element, or otherwiseformed by casting, molding, and other methods for forming a surfaceconfiguration. It is appreciated that angled grooves 400 a–k can beformed at various angles to the longitudinal axis L of implant 100 andto each other. For example, such angles can be less than 180 degrees.

In this embodiment of surface configuration 420, angled grooves 440 a–khave a V-shaped horizontal cross-section. Each surface projection 422has left and right side facets 432 and 434 that are convergent and forma high point or peak 436 at the top of each surface projections 422.Each peak 436 can be aligned along lines that are horizontally,longitudinally, and/or diagonally oriented along implant 100. The leftand right side forward and rearward facets 450, 452, 454, 456 functionto prevent side-to-side motion of implant 100 after it is inserted intothe implantation space. Peaks 436 may also function like teeth to engagebone B adjacent to the implant in the implantation site.

FIG. 19B shows a variation of second and third surface projections 460′,470′ that can be cleaved in one or more directions to increase thenumber of exposed sides of each projection and thus increase the surfacearea of the implant bone engaging surface available to contact bone B. Apreferred embodiment of this variation of the second and third surfaceprojections 460′, 470′ are cleaved by a longitudinal groove.

As shown in FIGS. 20–23, a fifth embodiment of the surface configurationof the present invention is generally referred to by the numeral 520.Surface configuration 520 includes surface projections 522 to facilitateinsertion of implant 100 into an implantation site while resistingexpulsion of implant 100 in a direction opposite to the direction ofinsertion. Surface projections 522 can be cleaved in one or moredirections to increase the number of exposed sides of each projectionand thus increase the surface area of the implant bone engaging surfaceavailable to contact bone B. For example, the surface projections can becleaved by a longitudinal cut 540 generally parallel to the longitudinalaxis L of implant 100 to form a surface projection having nine exposedsides. The surface projections may further be cleaved by a horizontalcut 542 generally perpendicular to the longitudinal axis L of implant100 to form a surface projection having eighteen exposed sides. The cutscan penetrate the surface projection at a depth substantially equal tothat of the height of the surface projections as measured from the upperor lower surfaces of the implant. The cuts can be oriented along atleast one of the longitudinal axis of the implant, an axis perpendicularto the longitudinal axis of said implant, and an axis at an anglebetween the longitudinal axis and the axis perpendicular to thelongitudinal axis of the implant. It is appreciated that cuts 540 and542 may be formed as part of the molding process for forming the surfaceprojections.

When cleaved by longitudinal cut 540 and horizontal cut 542, each ofsurface projections 522 has angled forward facet 524 a, 524 b directedat least in part toward leading end 502 of implant 100 and rearwardfacets 526 a, 526 b directed at least in part toward trailing end 504 ofimplant 100. Forward facet 524 has a length greater than the length ofrearward facet 526. Rearward facets 526 a, 526 b have a slope that issteeper than the slope of forward facets 524 a, 524 b. The cleavedportion of surface projection 522 can be spaced apart by a predetermineddistance and the space can be at least in part flat, curved, or anyother surface configuration suitable for the intended use. In thisembodiment, the base of rearward facets 526 a, 526 b forms an angle ofapproximately 45 degrees with respect to exterior surface 506 of implant100. Each one of surface projections 522 has left side facets 532 a, 532b and right side facets 534 a, 534 b directed toward the sides ofimplant 100, and forward facets 524 a, 524 b and rearward facet 526 a,526 b. In this embodiment of surface configuration 520, longitudinalgrooves 530 have a V-shaped horizontal cross-section and each surfaceprojection 522 has left and right side facets 532 a, 532 b, 534 a, 534 bthat converge toward one another. The left and right side facets 532 a,532 b, 534 a, 534 b resist side-to-side motion of implant 100 after itis inserted into the implantation space.

The surface configuration of the present invention can be formed bymolding, machining or otherwise. A preferred surface configuration ofthe present invention may readily be machined by milling from side toside, across the bone engaging surfaces, surface projections. A millingmachine with a cutting tool having an angled cutting face such as aV-shaped profile can then be run through the plurality of surfaceprojections parallel to the longitudinal axis of the implant to form theabove-described surface. In a preferred embodiment, the V-shaped cuttingtool of the milling machine has faces with an angle of approximately 90degrees, which faces are at a 45-degree angle to the plane of thesurfaces being so machined. Without departing from the presentinvention, the angle of the cutting faces can be more or less than 90degrees, the angle of the cutting face to the surface to be cut can bemore or less than 45 degrees, and rather than running the cutter elementparallel to the longitudinal axis of the implant, the cutting elementmay be run at an angle. By way of example only and not limitation, thisangle may be at 45 degrees to the longitudinal axis of the implant andeach surface projection can be formed by two grooves crossing theprojections at a 90 degree angle to each other.

The orthopedic implants of the present invention are made of artificialor naturally occurring materials suitable for implantation in the humanbody. The implants can comprise bone including, but not limited to,cortical bone, materials other than bone, such as metals including, butnot limited to, titanium and its alloys or ASTM material, surgical gradeplastics, plastic composites, ceramics, or other materials suitable foruse as an orthopedic implant. The implants of the present invention canfurther comprise or be combined with bone growth promoting materials,including but not limited to, bone, bone morphogenetic proteins,hydroxyapatite, and genes coding for the production of bone. Theimplants can be treated with a bone growth promoting substance, can be asource of osteogenesis, or can be bioabsorbable at least in part. Theimplants of the present invention can be formed of a porous material.

The orthopedic implants of the present invention can be for the purposeof achieving fusion. The exterior surface of the fusion implants caninclude at least one opening to permit for the growth of bone from boneor bone portion to adjacent bone or bone portion through the implant.The implant can have an internal chamber and may also have an accessopening for accessing the internal chamber, in which case the implantcan further have a cover such as a cap to close the access opening atleast in part. Openings in the exterior surface of the implant cancommunicate with the internal chamber to permit further growth of bonethrough the implant. The internal chamber can contain bone growthpromoting materials, including but not limited to, bone, bonemorphogenetic proteins, hydroxyapatite, and genes coding for theproduction of bone. The implants of the present invention can be formedof a material that intrinsically participates in the growth of bone fromone of the adjacent bones or bone portions to the other of the adjacentbones or bone portions.

While various embodiments of the present invention are presented by wayof example only and not limitation, common to each of them, is that theconfiguration of the surface is based on a plurality of surfaceprojections disposed in arrays, each surface projection comprising atleast one leading facet and at least one opposing trailing facet, inwhich the leading facet has a length greater than the trailing facet andthe trailing facet has a steeper slope than the slope of the leadingfacet. The surface configuration is located on at least a portion ofexterior bone engaging surface of the orthopedic implant.

While the implant shown in FIGS. 1, 2, and 3 is a hip prosthesis, it isappreciated that the surface configuration of the present invention isapplicable to any orthopedic implants having an exterior surfaceincorporating the present inventive teachings for engaging boneincluding but not limited to, any artificial joint component having anintramedullary stem, such as but not limited to, hip replacements,shoulder replacements, knee replacements, and finger joints; and medicalprosthetic implants for replacing a lost portion of a long bone.

It is believed that the operation and construction of the presentinvention will be apparent from the foregoing description and, while theinvention shown and described herein has been characterized asparticular embodiments, changes and modifications may be made thereinwithout departing from the spirit and scope of the invention as definedin the following claims.

1. A method for forming an interbody orthopedic implant having anexterior surface with a plurality of surface projections adapted forcontact with bone, including adjacent bones and bone portions, themethod comprising the steps of: providing the implant comprising aleading end for introduction of the orthopedic implant into the bone, anopposite trailing end, spaced apart sides therebetween, and amid-longitudinal axis passing through the leading and trailing ends, anexterior surface between said leading and trailing ends and said spacedapart sides; and forming surface projections as part of the exteriorsurface of the implant: at least a first and a second surface projectioneach having a first facet configuration with at least one forward facetdirected at least in part toward the leading end and at least onerearward facet directed at least in part toward the trailing end, saidforward facet and said rearward facet having a length and a slope, thelength of said forward facet being longer than the length of saidrearward facet, the slope of said rearward facet being steeper than theslope of said forward facet, said first and second surface projectionseach having a peak along a first line that is transverse to themid-longitudinal axis of said implant; and at least a third and a fourthsurface projection each having a second facet configuration with atleast one forward facet directed at least in part toward the leading endand at least one rearward facet directed at least in part toward thetrailing end, said forward facet and said rearward facet of said secondfacet configuration having a length and a slope, the length of saidforward facet of said second facet configuration being longer than thelength of said rearward facet of said second facet configuration, theslope of said rearward facet of said second facet configuration beingsteeper than the slope of said forward facet of said second facetconfiguration, said third and fourth surface projections each having apeak along a second line that is transverse to the mid-longitudinal axisand off-set from the first line transverse to the mid-longitudinal axis,the second facet configuration of the third and fourth surfaceprojections being different from the first facet configuration of thefirst and second surface projections.
 2. The method of claim 1, whereinthe step of forming includes at least one of the sub-steps of grinding,milling, burning, lasering, burnishing, electric discharge machining,broaching, and machining to form said surface projections.
 3. The methodof claim 1, wherein the steps of providing and forming include thesub-step of casting to form said implant with said surface projections.4. The method of claim 1, wherein said forming step includes thesub-step of orienting said surface projections relative to one anotherto form an array over at least a portion of said exterior surface ofsaid implant.
 5. The method of claim 1, wherein said forming stepincludes the sub-step of orienting said surface projections to begeometrically disposed relative to one another over at least a portionof said exterior surface of said implant.
 6. The method of claim 1,wherein the step of providing the implant includes providing an implanthaving at least one opening in each of the upper and lower surfaces incommunication with one another, the openings being configured to permitfor the growth of bone from vertebral body to adjacent vertebral bodythrough the implant.
 7. The method of claim 6, further comprising thestep of combining the implant with at least one of bone, bonemorphogenetic proteins, hydroxyapatite, and genes coding for theproduction of bone.
 8. The method of claim 6, wherein the step ofproviding the implant includes providing an implant having an internalchamber between the upper and lower surfaces and in communication withthe at least one opening in each of the upper and lower surfaces, theinternal chamber being adapted to contain bone growth promotingmaterials.
 9. The method of claim 1, wherein at least a fifth and asixth of said surface projections formed during the step of forming eachhave a third facet configuration with at least one forward facetdirected at least in part toward the leading end and at least onerearward facet directed at least in part toward the trailing end, saidforward facet and said rearward facet of said third facet configurationhaving a length and a slope, the length of said forward facet of saidthird facet configuration being longer than the length of said rearwardfacet of said third facet configuration, the slope of said rearwardfacet of said third facet configuration being steeper than the slope ofsaid forward facet of said third facet configuration, said fifth andsixth surface projections each having a peak along a third line that istransverse to the mid-longitudinal axis and off-set from the first andsecond lines, the third facet configuration of the fifth and sixthsurface projections being different from the first facet configurationof the first and second surface projections and the second facetconfiguration of the third and fourth surface projections.
 10. Themethod of claim 1, wherein the step of forming includes forming saidforward facets of said first and second surface projections to face thesame direction.
 11. The method of claim 1, wherein the step of formingincludes forming at least one of the surface projections along the firstline to have a maximum height from the exterior surface of the implantthat is substantially the same as the maximum height of one of thesurface projections along the second line.
 12. The method of claim 1,wherein the step of forming includes forming at least three surfaceprojections having the first facet configuration along the first lineand forming at least three surface projections having the second facetconfiguration along the second line.
 13. The method of claim 1, whereinthe step of forming includes forming at least four surface projectionshaving the first facet configuration along the first line and forming atleast four surface projections having the second facet configurationalong the second line.
 14. The method of claim 1, wherein the step offorming includes forming at least five surface projections having thefirst facet configuration along the first line and forming at least fivesurface projections having the second facet configuration along thesecond line.
 15. A method for forming an interbody orthopedic implanthaving a plurality of surface projections adapted for contact with bone,including adjacent bones and bone portions, the method comprising thesteps of: providing the implant comprising a leading end forintroduction of the orthopedic implant into the bone, an oppositetrailing end, and spaced apart sides therebetween, opposite upper andlower surfaces between said leading and trailing ends and said spacedapart sides, an exterior surface between said leading and trailing endsand said spaced apart sides; and forming a plurality of surfaceprojections as part of the exterior surface of the implant, each of thesurface projections having a base, at least two of the surfaceprojections each having at least one forward facet directed at least inpart toward the leading end and at least one rearward facet directed atleast in part toward the trailing end, said rearward facet terminatingat a first location proximate the base, said rearward facet terminatingat a second location proximate said forward facing facet, the firstlocation being closer to the leading end of the implant than the secondlocation, each of said at least two surface projections being formed tohave opposed side facets extending from the base and being directedgenerally toward said spaced apart sides of the implant, respectively,said side facets being located between said forward facet and saidrearward facet of each of said at least two surface projections.
 16. Themethod of claim 15, wherein the step of forming includes one of thesub-steps of grinding, milling, burning, lasering, burnishing, electricdischarge machining, and broaching to form said surface projections. 17.The method of claim 15, wherein the steps of providing and forminginclude the sub-step of casting to form said implant with said surfaceprojections.
 18. The method of claim 15, wherein said forming stepincludes the sub-step of orienting said projections relative to oneanother to form an array.
 19. The method of claim 15, wherein saidforming step includes the sub-step of orienting said projections to begeometrically disposed relative to one another.
 20. The method of claim15, wherein said side facets have a maximum width therebetween at thebase, the base of at least one of said surface projections being spacedapart from a base of another of said surface projections by a distanceno greater than one-half the maximum width of at least one of said atleast two surface projections.
 21. The method of claim 15, wherein thestep of forming includes forming the forward facets of at least two ofsaid at least two surface projections to face the same direction. 22.The method of claim 15, wherein the step of forming includes formingsaid side facets of each of said at least two surface projections toconverge toward each other in a direction away from the base.
 23. Themethod of claim 15, wherein the step of forming includes forming said atleast two surface projections to have substantially the same maximumheight from the surface of said implant.
 24. The method of claim 15,wherein the step of providing the implant includes providing an implanthaving at least two openings in said exterior surface in communicationwith one another, the openings being configured to permit for the growthof bone from one bone portion to another bone portion through theimplant.
 25. The method of claim 24, further comprising the step ofcombining the implant with at least one of harvested bone, bonemorphogenetic proteins, hydroxyapatite, and genes coding for theproduction of bone.
 26. The method of claim 24, wherein the step ofproviding the implant includes providing an implant having an internalchamber in communication with the at least two openings in said exteriorsurface, the internal chamber being adapted to contain bone growthpromoting materials.
 27. The method of claim 26, further comprising thestep of combining the implant with at least one of harvested bone, bonemorphogenetic proteins, hydroxyapatite, and genes coding for theproduction of bone.
 28. The method of claim 15, wherein the step offorming the plurality of surface projections includes using a millinginstrument.
 29. The method of claim 28, wherein the milling instrumentincludes a cutting tool with a V-shaped profile.